puzzle
noun.
a particularly baffling problem that is said to have a correct solution
he loved to solve chessmate puzzles|that's a real puzzler
Synonym: mystifier, puzzler, teaser
noun.
a game that tests your ingenuity
verb.
be a mystery or bewildering to
This beats me!|Got me--I don't know the answer!|a vexing problem|This question really stuck me
Synonym: mystify, nonplus, perplex, pose, stick, stupefy, gravel, get, flummox, dumbfound, bewilder, beat, baffle, amaze, vex
verb.
be uncertain about; think about without fully understanding or being able to decide
We puzzled over her sudden departure